Packaged terminal air conditioning (PTAC) units are typically used for cooling air within a space. In a particular embodiment, PTACs can be used to provide space cooling for the hotel industry, which permits the occupant to control of his/her own cooling and heating requirements. PTACs are thermostatically controlled to maintain the desired temperature in the space but have no means to condition outside makeup air nor to maintain humidity levels within the space.
PTACs typically provide unconditioned outside air to hotel rooms or other spaces through an opening in the back of the unit. The air is introduced to the space at ambient outside air temperatures and is not conditioned in any way to prevent high moisture levels within the space. This results in the potential for mold and mildew growth within the space, a recurring problem within the HVAC and hotel/motel industries for many years, especially in areas of the world where high outdoor air humidity levels are common, such as the southeastern portion of the United States. Mold and mildew growth is further propagated by the use of constant exhaust systems such as are found in many hotel rooms.
In hotel rooms where the exhaust is intermittent, for a typical PTAC unit in the cooling mode with its evaporator fan and the exhaust fan off, the outside air is drawn into the space by the negative pressure created by the fan. In this the outside air is intermittent and does not meet the requirements of ASHRAE Standard 90.1 and many local building codes. Additionally, the air remains at the outside air temperature and humidity level.
In hotel rooms where the exhaust is constant, a typical PTAC unit, whether on or off, will introduce unconditioned outside air to the space on a continuous basis. While this mode of operation meets the intent of ASHRAE Standard 90.1 and local building codes, the air continues to be introduced to the space at the outside air temperature and humidity level.
Therefore, it would be desirable to provide a packaged terminal air conditioning unit that is capable of conditioning and dehumidifying outside makeup air introduced to the space served.